1. Field of the Invention
This invention relates to an optical card processing apparatus which uses a light beam to record information on and/or reproduce information from a card-shaped recording medium.
2. Description of Related Art
As shown in FIG. 7, a conventional optical card processing apparatus of this type includes a card holder 9 having a card holding section 90 on its top side, and a guide mechanism 91 on which the card holder 9 is reciprocatively mounted. The card holding section 90 is provided with strip-shaped card retaining plates 93 on both sides of the top of a card support plate 92, as shown in FIG. 8, and card insertion grooves 94 are formed between the card retaining plates 93 and the top side of the card support plate 92. When both side edges of an optical card 8 are inserted into the guide insertion grooves 94, these side edges of the optical card 8 are held in a pressed state to secure the card.
A reversibly rotatably drive motor 96 is connected to the card holder 9 via a belt 95. Situated above the card holder 9 is an optical head 97 for recording information on and/or reproducing information from the optical card 8. The optical head 97 has an objective lens (not shown) whose focusing is controlled in such a manner that an irradiating beam produced at recording/reproduction has its focal point formed on the surface of the information recording medium of the optical card 8 at all times. Accordingly, when the card holder 9 is reciprocated relative to the optical head 97 by the drive motor 96, recording information on and/or reproducing information from an information track of the optical card 8 is carried out while focusing control is performed in such a manner that a fluctuation in the distance between the card surface and the objective lens is made to approach zero. Such fluctuation is caused by deformation of the optical card 8 and vibration of the the same that occurs when the card holder is reciprocated.
FIG. 9 illustrates the entirety of the optical card 8 as well as a portion of the card shown in enlarged form. The optical card 8 undergoes a data reading (reproduction) or data writing (recording) operation performed by an optical processing apparatus. The optical card is not limited to that of the type which undergoes recording/reproduction optically but also covers optical cards of the type subjected to recording/reproducing electromagnetically. An information recording zone 80 of the optical card 8 is provided with a number of information recording tracks 81 defined by track guides 82. Bits representing information are recorded on these tracks 81 in the form of pits (in the case of a card capable of undergoing recording/reproduction optically). The track guides 82 are for the purpose of causing the recording/reproduction optical head to follow the tracks on the card (tracking control).
Since the card holder 9 is so arranged that the two longitudinal side edges of the four edges of the optical card 8 are held by the retaining plates 93, the front and rear edges of the optical card 8 are the free edges when the card is being held by the card holder 9. Consequently, in the event that the optical card sustains warping or curvature in such a manner that its four sides rise, as shown in FIG. 10a, or in such a manner that its front and rear side edges bow upwardly, as depicted in FIG. 10b recording/reproduction performance suffers. Specifically, the curvature cannot be corrected by the card holding section 90 and a large focal-point error is produced by such buckling at the time of recording/reproduction.
FIG. 8 illustrates the warped optical card 8 in a state held by the card holder 9. The state of the information recording zone 80 of the optical card 8 which appears between the retaining plates 93 is such that portions A, B near the front and rear edges of the card rise while the central portion C is recessed.
FIG. 11 illustrates conditions under which focal-point error is produced when reproducing recorded information from the optical card 8 wrapped as shown in FIG. 8. It will be appreciated that focal-point error fluctuates in dependence upon the deformation at the front and read edge portions A, B and the central portion C.
When the optical card 8 warped in this manner is conveyed back and forth, the degree of card vibration is great and therefore the focusing control mechanism within the optical head 97 cannot follow up the vibration. The result is a large focal-point error and poor recording/reproduction performance. In order to suppress the occurrence of this vibration, it is necessary to reduce the speed at which the card holder 9 is fed, but this makes it difficult raise the speed of the recording/reproduction operation.